1. Field of Invention
The embodiments of the present invention relate to a writing implement comprising an ink reservoir, a writing tip and a venting device for the reservoir.
2. Description of the Related Art
The reservoir-venting device acts as an ink buffer. It allows any overflow of some of the ink contained in the reservoir, which would otherwise spread outside the implement through the writing tip, to be absorbed. Such an overflow of ink can be caused, for example, by a temperature variation due to prolonged contact with a user's hand. It can also be caused by excessive pressure in the reservoir, due to the writing implement being struck.
Moreover, when the writing implement is in use, the ink flows from the reservoir to the tip, and emerges from the tip when the latter is moved over a writing medium, such as a sheet of paper. The reservoir is then progressively emptied of the ink, and it is necessary to allow a volume of air equivalent to that of the consumed ink to enter the reservoir in order to prevent the flow of ink from stopping. Another function of the reservoir-venting device is therefore to equalize the pressure in the latter vis-à-vis the air pressure outside the writing implement, such that the ink continues to flow by capillarity from the reservoir to the writing tip.
Several embodiments of a reservoir-venting device are known. Reservoir-venting devices are known, in particular from documents U.S. Pat. No. 4,556,336 and U.S. Pat. No. 6,474,894, which comprise a set of zigzags. The set of zigzags forms a labyrinth which connects the ink reservoir to an orifice open to the outside of the implement. It is formed by a plastic part, which is generally moulded. The absorption of an overflow of ink is achieved by a precise adjustment of the capillarity of the ink in the zigzags. The ink can enter the zigzags, but this entry is limited by capillary forces exerted on the ink by the walls of the zigzags. A drawback of such devices results from the complex shape of the part which defines the zigzags. The moulding of this part is difficult to carry out, and results in a significant additional manufacturing cost for the writing implement.
The document US-A-2003/0231921 discloses another embodiment of a venting device for the ink reservoir. The device comprises a cavity which is filled with a porous element having open porosity. Like the set of zigzags in the previous case, the cavity is in communication, on the one hand with the ink reservoir and on the other hand with an orifice which opens to the outside of the implement. The operation of such a device is based on the capillarity of the ink in the pore volume of the element. However, reproducible large-scale production of a porous element having a specific open porosity is difficult. Its manufacture thus contributes to an increase in the cost price of the writing implement.